Cleanup

I published a couple of changes based on API cleanups we performed this week.

I was surprised to notice how close the design of this library is to the design of the new [ruby client](github.com/aetrion/dnsimple-ruby) and the [go client](https://github.com/weppos/go-dnsimple).

Specifically, I introduced the "proxy" pattern in the Ruby client

```ruby
client.domains.list
client.domains.list_records
```

and I was surprised to see how closely it matched this library. Some of the changes are on the direction to make this library homogeneous with the Ruby lib and the docs.

Thanks for your great work!